using System;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Security;


namespace Org.BouncyCastle.Crypto.Paddings
{

	/**
	* A padder that adds ISO10126-2 padding to a block.
	*/
	public class ISO10126d2Padding: IBlockCipherPadding
	{
		private SecureRandom random;

		/**
		* Initialise the padder.
		*
		* @param random a SecureRandom if available.
		*/
		public void Init(
			SecureRandom random)
			//throws ArgumentException
		{
			this.random = (random != null) ? random : new SecureRandom();
		}

		/**
		* Return the name of the algorithm the cipher implements.
		*
		* @return the name of the algorithm the cipher implements.
		*/
		public string PaddingName
		{
			get { return "ISO10126-2"; }
		}

		/**
		* add the pad bytes to the passed in block, returning the
		* number of bytes added.
		*/
		public int AddPadding(
			byte[]	input,
			int		inOff)
		{
			byte code = (byte)(input.Length - inOff);

			while (inOff < (input.Length - 1))
			{
				input[inOff] = (byte)random.NextInt();
				inOff++;
			}

			input[inOff] = code;

			return code;
		}

		/**
		* return the number of pad bytes present in the block.
		*/
		public int PadCount(byte[] input)
			//throws InvalidCipherTextException
		{
			int count = input[input.Length - 1] & 0xff;

			if (count > input.Length)
			{
				throw new InvalidCipherTextException("pad block corrupted");
			}

			return count;
		}
	}

}
